I recently stated that the 9.75" axle is part of the Heavy Duty Payload Package, which isn't available on any trim level above the base Lariat. While I still believe that is true, it appears I was mis-interpreting things. There is evidence emerging that the 9.75" axle isn't just part of the Heavy Duty Payload Package, but that there are other ways of getting it as well as two forms of "it".

First, advocate posted the following on this thread:
Second, this Ford document on specifications for the 2015 F150, which has lots of neat info, has a couple of interesting points for this thread. Here's a shot of the page on rear axles and, as I've circled in green, there are actually 3 axles used: The 8.8, a 9.75, and a 9.75 HD. And, it looks to me like any time you get the electronic-locking differential you get the 9.75" - either the standard or the HD one.





Also, there is apparently a difference in the frame for at least the Heavy Duty Payload Package, as shown here in the footnotes from the same document: (Note the "3.5L 4V V6? )



And, here are the frame spec's from the same doc. I haven't figured out which trucks get the HPP frames, but I'd bet the HD Payload trucks do. However, I can't reconcile this, yet, with the above statement that the HD frame gets an upgrade to .150" rail thickness. According to this there are three different frames - LD, HD, and HPP. Anyway, the rail goes from .087" for the LD to .110" for the HPP, which is an upgrade of .023". So I can't find a .150" frame rail - maybe it is a mis-print like the "4V" on the 3.5L?




So, what is "HPP"? That doesn't seem to be defined in that document, but if you go to Ford's Body Builder's Layout Book you'll see that's their terminology for Heavy Payload, which is surely the Heavy Duty Payload Package.

 

Well, there have been 85 views of this but no responses. So, maybe I put too much in one post? (It actually kept growing, and growing, and...) Given that, let me summarize and see if any of you agree or disagree:

• Diff's: There are 3 different differentials being used in the 2015 F150's:
  1. 8.8": The standard diff that runs the gamut of ratios from 3.31 to 3.73 but doesn't have the electronic locking
  2. 9.75": The step up diff, again running the range from 3.31 to 3.73, but with e-lock.
  3. 9.75" HD: The heavy-duty diff for, presumably, the HD Payload Package vehicles and only comes with 3.73 ratio and e-lock
• Frames: There are 3 different frame strengths being used in the 2015 F150's, with the following max side rail thicknesses:
  1. .087": These are the light-duty frames
  2. .100": Heavy-duty frames
  3. .110": Heavy-duty Payload Package frames

So, what did I miss? What did I state incorrectly?

 

The way i interpret that chart, it looks like the 8.8 and 9.75 is available with or without the e locker, but the 9.75hd is only available with the e locker.

 

Good! Someone responded! Thanks.

I see what you mean. They said "Standard/Electronic-locking" when they could have said "Standard" over one column and "Electronic-locking" over the next one. That would suggest as you said that you can have the 8.8's and the 9.75's either way while the 9.75HD's only come with e-locks. Interesting. Thanks.

Also, did anyone note a couple of other anomalies:

• The 8.8 is available with a 3.31 in the 4x2's but not in the 4x4's
• The 9.75 is available with a 3.15 ratio in the 4x2's but not in the 4x4's. Instead it goes to a 3.31 as the tall gear.

 

The 3.15 has always been the base gear for the 4x2 and the 3.31 for the 4x4 trucks.

The 8.8 was the only offering in the pre '97 F-150's and it was a very stout rear end. I see no issues here.

 

Right on Tim. Have any of y'all boys ever known of a differential failure? Kind of like engines blowing to smithereens because of bad oil. I've never known it to happen.

 

The 8.8 may be stout, but Ford doesn't think it is stout enough to pull 12,200 lbs or they wouldn't put the 9.75 in for the higher load trucks.

As for a differential failure, I have two 81's with the 9", the big brother to the 8.8, and both had diffs that failed. Rusty's was abuse by the PO, and the other was in Dad's truck and it had plenty of lube all its life. But the wear and tear of towing a travel trailer many thousands of miles took its toll and the ring and pinion had to be replaced.

So yes, I've known of differential failure, and in diffs bigger than the 8.8" and with engines that put out less torque than the 3.5L EB does. I plan to use my truck to tow many miles and was worried about the durability of the 8.8" diff - especially given the 420 lb-ft capability of the 3.5L EB, which will get used frequently. But now that I realize they are installing the 9.75 I'm a lot happier.

 

Sounds good, Gary. Ye've done ye homework!

 

The diff in my old '88 came apart at 250K miles. I beat the snot out of that truck too.

The 8.8 isn't rated to pull 12,200 lbs so that's a moot point. But, what concerns me is the unsuspecting truck buyer who didn't do all of his homework, buys a truck with an 8.8 and decides that he can pull 12K. His fault totally. I still think Ford should stick with the 9.75 across the board.

 

It will be his/her fault as each truck carries a max GVWR as well as a GCWR, beyond which one should not go. But, I'm sure there will be many that go well beyond it 'cause Ford advertised that the 2015 F150 can tow 12,200 lbs and carry 3,300 lbs. Of course, they don't read the fine print that says you have to start with the #'s on the truck instead of the advertising, then you have to subtract all of the "stuff" you are carrying, as well as......

 

you guys DO know that this isn't really the same 8.8" that was in the older trucks right? Might be the same ring and pinion, axle shafts, etc, but the housing looks substantially beefier. First time I saw one I swore it was a new diff that Ford started using...figured they went away from corporate diffs and started buying third party.

 

I found this at 2015 Ford F-150 First Drive - Making HistorySo, while the axles and maybe the bearings are larger, the ring and pinion are apparently the same. That means the axle's ability to support a load is greater, but the ability to handle torque hasn't changed. And it would seem its torque capacity is below the output of the 3.5L EB.

 

My truck is 2015xlt sport with 5.0 4x4 it has 8.8 with 3.31
I guess this is one more misprint from Ford

 

Apparently so. I'm used to similar mis-prints in the 5000+ page master parts catalog for the 80-89 trucks, bud had assumed that short documents like this one would be better vetted.

 

They happen, but it's not real common.

I think it's highly unlikely that you're going to damage an 8.8" axle by pulling 12,000 lbs. The axle is still rated to take the maximum power the engine produces. Towing heavy could mean a greater load on the rear axle as well as heat buildup as more power is used to keep it going down the road though. If you're towing at high speed across I-10 in the summertime you may have a problem.

I don't think the ring and pinion gear are the limiting factor here. Have you ever seen or heard of someone breaking the gears? I haven't, but bearing failures can happen. If those are upsized to handle the increased loading I don't see the issue.